The goal of this project is to define the interactions of selenium and vitamins C and E in preventing oxidant damage. Vitamin C recycles and thus preserves vitamin E or alpha-tocopherol in cell membranes. We showed that the selenoenzyme thioredoxin reductase, which is present in both cytosol and mitochondria, recycles vitamin C from both its oxidized forms. We hypothesize that thioredoxin reductase and vitamin C spare vitamin E in part through these mechanisms, and that vitamin C and other selenoenzymes also directly consume radicals that would otherwise oxidize vitamin E. This hypothesis is supported by two in vivo guinea pig models developed in the first project period. In one model, a combined deficiency of vitamins E and C produces rapidly fatal central nervous system (CNS) dysfunction. In the other model, a combined deficiency of vitamin E and selenium causes a rapidly fatal myopathy. In the latter model, mitochondrial degeneration precedes muscle necrosis. This suggests that mitochondrial integrity depends on adequacy of both vitamin E and selenium. In this project, we will test this hypothesis directly, and determine as well whether vitamin C contributes to mitochondrial function and defense against oxidant stress. Given the recent evidence that mitochondrial dysfunction leads to apoptosis, assessing the role of antioxidant vitamins and selenium in protecting mitochondria from oxidant damage will have relevance for aging and human diseases, such as atherosclerosis and neurodegenerative disorders. There are four specific aims involving guinea pigs, which, like humans, cannot synthesize vitamin C de novo. Prompted by the results of the in vivo model of combined deficiencies of vitamin E and selenium, the first three aims involve studies in mitochondria prepared from guinea pig muscle. In the first aim, uptake, recycling, function, and antioxidant role of vitamin C in mitochondria will be assessed. In the second aim, the distribution, recycling, and antioxidant function of vitamin E in mitochondria will be determined. In the third aim, the role of selenium in preventing mitochondrial oxidant damage will be assessed. In the fourth aim, the specificity of different forms of vitamin E in preventing muscle and CNS damage will be determined in vitamin E-deficient guinea pigs. Whether selenium and ascorbate spare vitamin E in vivo will also be assessed. Using this approach, it will be possible to relate the crucial, mitochondrial functions of selenium and vitamins C and E to the antioxidant defenses of the whole animal.